It is well known in the art of ignition systems for automotive vehicles to have an ignition coil that produces magnetic energy upon discharge to create a high voltage spark to initiate combustion in an engine cylinder. Permanents magnets may be used to bias the core in the ignition coil to permit an increase in the stored magnetic energy in a magnetic circuit of the ignition coil.
Typically, an ignition coil includes primary and secondary windings each wound around a spool and disposed about a cylindrical magnetic core with the primary winding surrounding the secondary winding. Cylinder shaped permanent magnets are disposed at the ends of the magnetic core. To make this type of ignition coil compact, the magnetic core is made smaller than in other types of ignition coils. However, one drawback with this type of ignition coil is that, due to the levels of bias required with the small cores, the magnets have to have a very high energy product. This requirement limits the useable material for the magnets to materials like sintered neodymium-iron-boron (NdFeB) and samarium-cobalt (SmCo). The sintered magnets have a very low resisitivity, 2.times.10.sup.-4 ohm-cm, which yields high eddy current losses in the magnets. Usually, the diameter of the magnets is the same as the diameter of the magnetic core and they are typically 4 to 5 mm long. This creates a large eddy current path around the diameter of the magnets, resulting in an eddy current loss that is proportional to the diameter squared. In some coil designs, 15 to 20% of the energy lost is due to the eddy current losses in the magnets. There is a need to reduce the magnet eddy current losses to improve the efficiency of the ignition coil.